Towards long lasting zirconia-based composites for dental implants: Transformation induced plasticity and its consequence on ceramic reliability

Abstract

Zirconia-based composites were developed through an innovative processing route able to tune compositional and microstructural features very precisely. Fully-dense ceria-stabilized zirconia ceramics (84vol% Ce-TZP) containing equiaxed alumina (8vol%Al₂O₃) and elongated strontium hexa-aluminate (8vol% SrAl₁₂O₁₉) second phases were obtained by conventional sintering. This work deals with the effect of the zirconia stabilization degree (CeO₂ in the range 10.0-11.5mol%) on the transformability and mechanical properties of Ce-TZP-Al₂O₃-SrAl₁₂O₁₉ materials. Vickers hardness, biaxial flexural strength and Single-edge V-notched beam tests revealed a strong influence of ceria content on the mechanical properties. Composites with 11.0mol% CeO₂ or above exhibited the classical behaviour of brittle ceramics, with no apparent plasticity and very low strain to failure. On the contrary, composites with 10.5mol% CeO₂ or less showed large transformation-induced plasticity and almost no dispersion in strength data. Materials with 10.5mol% of ceria showed the highest values in terms of biaxial bending strength (up to 1.1GPa) and fracture toughness (>10MPa√m). In these ceramics, as zirconia transformation precedes failure, the Weibull modulus was exceptionally high and reached a value of 60, which is in the range typically reported for metals. The results achieved demonstrate the high potential of using these new strong, tough and stable zirconia-based composites in structural biomedical applications.

Statement of significance: Yttria-stabilized (Y-TZP) zirconia ceramics are increasingly used for developing metal-free restorations and dental implants. Despite their success related to their excellent mechanical resistance, Y-TZP can undergo Low Temperature Degradation which could be responsible for restoration damage or even worst the failure of the implant. Current research is focusing on strategies to improve the LTD resistance of Y-TZP or to develop alternative composites with better stability in vivo. In this work the mechanical characterization of a new type of very-stable zirconia-based composites is presented. These materials are composed of ceria-stabilized zirconia (84vol%Ce-TZP) containing two second phases (α-alumina and strontium hexa-aluminate) and exhibit exceptional strength, toughness and ductility, which may allow the processing of dental implants with a perfect reliability and longer lifetime.

Keywords: Alumina; Composite; Mechanical properties; Plasticity; Zirconia.